Chemical Gnomonclature*

Scotoma is the technical term for the blind spot in our field of vision. Our brains interpolate the missing data so we don't perceive a black spot, but in fact we have two scotomas, caused by the lack of retinal cells where the optic nerve joins the retina (see link).

The Periodic Table is a reticulated array of data. In the mid 1930's, element 43 was still conspicuously lacking. Dmitri Mendeleev, that great Russian seer of visions and father of the Periodic Table, foresaw its existence and called it eka-manganese, meaning "one-after-manganese." Here's what the family of transition metals looked like in the mid 1930's:

Chemists sought eka-manganese unsuccessfully for 75 years after Mendeleev's prediction: their efforts are nicely summarized by van der Krogt. Of the fruitless efforts, those of Noddack et al. came closest, and they proposed the name masurium in 1925. Several Periodic Tables from that era even included Ma beneath manganese.

Unequivocal proof for element 43 appeared in 1937, after an Italian team led by Emilio G. Segrè  isolated it from radioactive samples of next door molybdenum which had been bombarded with deuterium nuclei at Berkeley. They named the new element technetium from the Greek τεχνητος, meaning artificial.
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*Gnomonclature is an homage to James Joyce who invented a literary device called gnomon to accentuate character or story element.  In the words of his character Stephen in A Portrait of the Artist as a Young Man:

Absence is the highest form of presence.

The absence of eka-manganese drove generations of chemists to search for it because it was there--somewhere.

Germanium Arrived According To Plan

Germanium is a metalloid and thus only a half-metal. Despite this, it was a "planned" element. By planned I mean that its existence was foretold by the father of the periodic table, Russian chemist Dmitri Mendeleev.

Mendeleev was not the first to bring rhyme and reason to the elements--first came columns--Döbereiner's triads, and later rows--Newlands' Law of Octaves. But Mendeleev properly put together the whole kahuna, or at least what was known at the time. More importantly, he correctly predicted elements. Here's what he knew and what he knew must exist in 1871:

Click to enlarge

It's hard to see, but Mendeleev left a blank: "--  = 72 " in Group IV.  He called the unknown element eka-Silicon meaning one below Silicon. Eka-Silcon was discovered in 1886 and had an atomic mass of 72.6 amu. Van der Krogt tells the story of naming Germanium here, along with some Roman history.

Mendeleev also predicted the existence of eka-Aluminum and estimated its mass as 68.  The element was discovered and named Gallium in 1875 and had an atomic mass of 69.7 amu. The agreement between theory and experiment was almost as astonishing as Bode's Law. But Mendeleev's table survived.